Electronic ballast with controlled lamp preheating

Abstract

An electronic ballast provides controlled preheating for a discharge lamp. A power converting circuit receives a DC power input and converts it into an AC power output. A starting circuit coupled to the power converting circuit generates a high voltage for starting the lamp. A control circuit controls the power converting circuit to generate AC power output to the lamp dependent on a mode of operation. A symmetry detecting circuit determines a positive-negative symmetrical state of the output power provided to the discharge lamp with respect to ground. The control circuit has a starting mode wherein the discharge lamp is triggered to start with a high voltage generated by the starting circuit, an electrode heating mode wherein the AC power output of the power converting circuit is controlled to a first frequency for heating each lamp electrode, and a steady-state mode wherein the AC power output of the power converting circuit is controlled to a second frequency for maintaining lighting of the discharge lamp. The control circuit shifts from the electrode heating mode to the steady-state mode when the symmetry detecting circuit determines that the AC power output is in a positive-negative symmetrical state in the electrode heating operation.

Description

CROSS-REFERENCES TO RELATED APPLICATIONS[0001]A portion of the disclosure of this patent document contains material that is subject to copyright protection. The copyright owner has no objection to the reproduction of the patent document or the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.CROSS-REFERENCES TO RELATED APPLICATIONS[0002]This application claims benefit of the following patent application(s) which is / are hereby incorporated by reference: Japan Patent Application No. JP2008-277424, filed Oct. 28, 2008.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0003]Not ApplicableREFERENCE TO SEQUENCE LISTING OR COMPUTER PROGRAM LISTING APPENDIX[0004]Not ApplicableBACKGROUND OF THE INVENTION[0005]The present invention relates generally to an electronic ballast for powering a discharge lamp. More particularly, the present invention relates to an electronic ballast h...

AI Technical Summary

Benefits of technology

"The present invention provides an electronic ballast that can set the duration of electrode heating operation for each discharge lamp to a suitable length. The ballast includes a symmetry detecting circuit to determine the state of power provided to the lamp. If the power is in a positive-negative symmetrical state, the ballast shifts to steady-state operation. The control circuit does not prematurely shift to steady-state operation even if the lamp current is unstable during the initial stages of operation. The control circuit can also stop outputting AC power when the duration of the electrode heating operation reaches the upper time limit without a determination of positive-negative symmetrical state, improving the ability of the ballast to restart. The control circuit counts the number of times the lamp is returned to the starting operation and stops outputting AC power when the number reaches a predetermined limit to prevent excessive electrical stress on the lamp and circuit components."

Problems solved by technology

This results in a lamp current becoming asymmetrical between polarities.

When the electrode heating operation shifts to the steady-state operation where the electrode of the discharge lamp is not sufficiently heated, as described above, discharge becomes unstable, thereby possibly causing fade-out.

However, where multiple discharge lamps may be connected to the ballast, a particular duration of the electrode heating operation that accommodates all discharge lamps is likely to be excessive for some of the lamps.

Images